Direct-positive silver halide emulsion containing halogen conductor and electron acceptor developed with polyhydroxy benzene

ABSTRACT

Process for developing blue-sensitve-direct-positive silver halide photographic elements with a polyhydroxybenzene developing agent wherein the silver halide emulsion of the element comprises fogged silver halide grains and an organic compound which accepts electrons, wherein said halide is at least 50 mole percent chloride and novel blue-sensitive-direct-positive emulsions which can be used in this process.

United States Patent Kirby M. Milton Fishers, N .Y.;

Inventors Bernard D. lllingsworth, deceased, late of Rochester, NY. by Mary D. lllingsworth,

executrix Sept. 9, 1968 Oct. 26, 197 1 Eastman Kodak Company Rochester, N.Y.

Appl. No. Filed Patented Assignee DIRECT-POSITIVE SILVER HALIDE EMULSION CONTAINING HALOGEN CONDUCTOR AND ELECTRON ACCEPTOR DEVELOPED WITH POLYHYDROXY BENZENE 23 Claims, No Drawings U.S. Cl

lnt. Cl Field of Search References Cited UNITED STATES PATENTS 6/1956 Hood et a1.

OTHER REFERENCES Derwent Belgian Patents Report, Oct. 18, 1967, No. 38/67, page 9, Belgian Pat. 695,363

Primary Examiner-Norman G. Torchin Assistant Examiner-W0n H. Louie, Jr.

Attorneys-W. H. J. Kline, Bernard D. Wiese and Gerald E.

Battist ABSTRACT: Process for developing blue-sensitve-directpositive silver halide photographic elements with a polyhydroxybenzene developing agent wherein the silver halide emulsion of the element comprises fogged silver halide grains and an organic compound which accepts electrons, wherein said halide is at least 50 mole percent chloride and novel blue-sensitive-direct-positive emulsions which can be used in this process.

DIRECT-POSITIVE SILVER HALIDE EMULSION CONTAINING HALOGEN CONDUCTOR AND ELECTRON ACCEPTOR DEVELOPED WITH POLYI'IYDROXY BENZENE This invention relates to photographic materials, their preparation and use. In one aspect, this invention relates to processing direct-positive lithographic elements. in another aspect this invention relates to new blue-sensitive-direct-positive silver chloride emulsions containing an electron acceptor and a halogen conductor.

in the graphic arts field, where it is desired to make photographic reproductions of line and halftone material, it is customary to employ silver halide. emulsions having extreme contrast. For this purpose, photographic silver chlorobromide emulsions are generally employed, the silver chloride content of the emulsions being at least about 50 mole percent. After exposure of the emulsions in the conventional way, either to a halftone negative or to an original through a vacuum contact screen, the emulsions are developed in a polyhydroxybenzene photographic developer having very low free sulfite contentl Development is believed to proceed catalytically, and such development is commonly referred to in the graphic arts field as infectious development." In order to control the amount of free sulfite in the developer, it is customary to employ sodium formaldehyde bisulfite in the developer which releases small amounts of sulfite to at least partially stabilize the developing solutions for short periods of time.

A disadvantage of the lithographic films which are currently available is that they are all negative working. In present systems, it is necessary to use a negative material in the camera, prepare a positive transparency from the negative print and then prepare the printing plate from the positive transparency. If a direct-positive, high-contrast material could be made with projection speed, it could be used in a camera to make direct-positive halftone reproductions which could then be used directly to prepare printing plates. lf a direct-positive camera speed film were available, therefore, it would eliminate a costly step in the prior art process.

It would also be desirable to provide a direct-positive lithographic material which will form a good image record with blue light. This would eliminate the need for filters and light sources for systems which require exposure with radiation from only selected regions of the spectrum.

According to this invention, we have now found a system for providing improved direct-positive lithographic film records. This objective has been accomplished by a process which comprises processing exposed, blue-sensitive-directpositive, high-contrast photographic elements in a photographic developer wherein the developing agent consists essentially of a polyhydroxybenzene compound. The directpositive emulsion utilized in the process comprises fogged silver halide grains and an organic compound which accepts electrons wherein said halide is at least 50 mole percent chloride.

in one preferred embodiment of this invention, the developer contains low concentrations of a sulfite to provide infectious" development.

Another preferred embodiment of this invention relates to blue-sensitive-direct-positive silver chloride emulsions comprising fogged silver halide grains in combination with an electron acceptor and a halogen conductor.

According to a highly preferred embodiment of the invention, the direct-positive emulsion has adsorbed to the fogged grains, in combination with an electron-accepting compound, a halogen conductor having an anodic polarographic half wave potential less than 0.85 and a cathodic polarographic half wave potential which is more negative than -1.0. These emulsions have an unusually high sensitivity or photographic speed. lfthe halogen-conducting compound does not have the polarographic half wave potential set forth above, the emulsions containing the compound will not have an unusually high sensitivity.

In another preferred embodiment, the direct-positive, silver halide emulsions of this invention comprise fogged silver halide grains and an organic compound which accepts electron, wherein said chloride is at least 50 mole percent chloride, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support, gives a maximum density of at least 1 upon processing for 6 minutes at about 68 F. in Developer A, has a maximum density which is at least about 30 percent greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Developer A after being bleached for about 5 minutes at about 68 F. in a 0.3 percent aqueous potassium ferricyanide solution.

DEVELOPER A N-methyl-p-aminophcnol sulfate 2.59 ascorbic acid l0.09

potassium metaborate 35.09 potassium bromide 1.09 water to l liter pH of 9.6

In another embodiment of the invention, certain high molecular weight organic compounds, particularly sulfonated compounds as described hereinafter, can be used in combination with electron-accepting compounds and/or halogen-conducting compounds to effect an even greater increase in photographic speed or sensitivity.

It has been found that through the above preferred embodiments a lithographic system has been provided which yields relatively high photographic speed, blue-sensitive, high-contrast lithographic records.

The photographic developer employed in our invention contains a silver halide developing agent consisting essentially of a polyhydroxybenzene compound. Examples of polyhydroxybenzene compounds are hydroquinone, catechol, pyrogallol, isopropylhydroquinone, methylhydroquinone, 2,5- dimethylhydroquinone, o-chlorohydroquinone, obromohydroquinone, 4-phenyl catechol, 4-phenethyl catechol, 4-phenpropyl catechol, 4-t-butyl catechol, 4-n-butylpyrogallol, 4,5'dibromocatechol, etc. Esters of such compounds, e.g., formates and acetates, can also be employed. The developer can be contained in the element, in the solution or can be supplied from a layer on a separate support. In one preferred embodiment of this invention, the developing agent consists essentially of 1,4-dihydroxybenzene compounds.

The developing agent can be employed in any concentration effective for the intended purpose. Generally, good results are obtained when the developer contains from about 12 to about 20 grams of developing agent per liter of developer.

The developer can contain conventional addenda such as antioxidants, e.g., sodium sulfite; alkaline material to produce pH of at least about 9.0, e.g., sodium carbonate, sodium hydroxide, etc.; restrainer, e.g., potassium bromide, sodium bromide; sequestering agents, etc. The use of a developer containing a carbonyl bisulfite-amine condensation product, with at least about 0.075 mole of excess free amine per liter of developer composition and a dihydroxybenzene developing agent as claimed in application, Ser. No. 583,935 filed Oct. 3, 1966, of my coworker Masseth, is also quite useful in my invention.

in a preferred embodiment of this invention, the developers contain (1) sodium formaldehyde bisulfite or a carbonyl bisulfite amine and (2) from about 0.01 to about 0.05 molar of sulfite ion. Generally this {developer has a pH of at least 9.0. The sodium formaldehydebisulfite can generally be used in the developer in concentrations of about 40 to about grams per liter and is preferably used in combination with an alkali metal sulfite; or it can also be formed in situ by employing a mixture of formaldehyde (or paraformaldehyde) and sodium white in the developer.

Alkylene oxides can also be utilized in one embodiment of this invention. Typical useful compounds include polyethylene glycol, polyethylene glycol oleyl ether, polyethylene glycol cetyl ether, polyethylene oxide derivatives, block copolymers such as those comprising blocks of polyoxypropylene, polyoxytehylene and the like, water-soluble organosilicone polyalkyleneoxide polymers and the like.

The direct-positive silver halide emulsions of this invention comprise fogged silver halide grains and an organic compound which accepts electrons. Emulsions of this type are blue-sensitive. It is understood that blue-sensitive means that directpositive compositions will provide a reversal image when exposed with light in the 350 to 500 millimicron range of the electromagnetic spectrum. The silver halide compositions can also be spectrally sensitized so as to form reversal images when exposed in other regions of the spectrum such as in the green and red regions. However, they all have the property of being capable of forming a reversal image when exposed with light in the blue region of the spectrum.

Suitable electron-accepting compounds which can be used in this invention include photoelectron-accepting compounds or desensitizing dyes. Compounds of this type include the known desensitizers which trap electrons, as disclosed in British Pat. 723,019, published Feb. 2, 1955. The electron acceptors which give particularly good results in the practice of this invention can be characterized in terms of their polarographic half wave potentials, i.e., their oxidation reduction potentials determined by polarography. Cathodic measurements can be made with a 1X10 molar solution of the electron acceptor in a solvent, for example, methanol which is 0.05 molar in lithium chloride using a dropping mercury electrode with the polarographic half wave potential for the most positive cathodic wave being designate E Anodic measurements can be made with 1X10 molar aqueous solvent solution, for example, methanolic solutions of the electron acceptor which are 0.05 molar in sodium acetate and 0.005 molar in acetic acid using a carbon paste of pyrolytic graphite electrode, with the voltammetric half peak potential for the most negative anodic response being designated E In each measurement, the reference electrode can be an aqueous silversilver chloride (saturated potassium chloride) electrode at 20 C. Electrochemical measurements of this type are known in the art and are described in New Instrumental Methods in Electrochemistry, by Delahay, lnterscience Publishers, New York, New York, 1954; Polarograplzy, by Kolthoff and Lingane, 2nd Edition, lnterscience Publishers, New York, New York, 1952; Analytical Chemistry, 36, 2426 (1964) by Elving; and Analytical Chemistry, 30, 1576 (1958) by Adams. Plus and minus signs are according to IUPAC (International Union of Pure and Applied Chemistry) Stockholm Convention 1953. Compounds which can be employed as electron acceptors in the practice of this invention include organic compounds having an anodic polarographic half wave potential u) and a cathodic polarographic potential (15,) which when added together give a positive sum. Preferably, such compounds also spectrally sensitize photographic silver halide emulsions to radiation having a wavelength of at least about 430 mu and generally spectrally sensitize such emulsions in the range of about 430 to about 800 mu. Advantageously, these compounds provide spectral sensitization such that the ratio of minus blue relative speed to blue relative speed is greater than 7 and preferably greater than 10 when exposed to a tungsten source through Wratten No. 16 and No. 35 plus 38A filters respectively and can be termed spectral sensitizing electron acceptors.

An especially useful class of electron-accepting compounds which can be used in the direct-positive photographic silver halide emulsions of this invention are cyanine dyes, particularly imidazoquinoxaline dyes, such as those described in Brooker et al., Belgian Pat. 660,253, published Mar. 15, i965. Very good results are obtained with cyanine dyes containing an indole nucleus aromatically substituted in the 2 position, i.e., a cyanine dye containing a 2-aromatically substituted indole nucleus. One useful class of spectral sensitizing electron (1) 1,1-dimethyl-2,2-dipheny1-3,3-indolocarbocyaulne bromide Icr1=oH- :H

' Ph Ph l i Me Me Br (2) 2,2-;i-p-methoxyphenyl-1,1-dln1ethyl-3,3-indolocarbocyarune bro- OMe M00 (3) 1,1-dimethyl-2,2,S-triphe11y1-3,3-indolocarbocyaninc perchlorate l CH=CHC III Ph Pl11 Me Me (4) 1,1-3,3-tetraethylimldazo[4,5-b]qulnoxalinocarbocynnlne chloride I t is IC \s w Et Additional examples include phenosafranine, pinacryptol yellit 01 low, S-m-nitrobenzylidenerhodanine, 5-m-nitrobenzylidene-3- phenylrhodanine, 3-ethyl-5-m-nitrobenzylidenerhodanine, 3- ethyl-5-(2,4'dinitrobenzylidene)rhodanine, 5-o-nitrobenzylidene-3-phenylrhodanine, l, 3-diethyl-6-nitrothia-2'-cyanine iodide, 4-nitro-6-chlorobenzotriazole, 3,3'-diethyl-6,6- dinitro-9-phenylthiacarbocyanine iodide, 2-(pdimethylaminophenyliminomethyl)benzothiazole ethoethyl sulfate, crystal violet, 3.3'-diethyl-6,6'-dinitrothiacarbocyanine ethyl sulfate, l',3-diethyl-6-nitrothia-2'-cyanine iodide, l,3-diamino-5-methyl-phenazinium chloride, 4-nitro- 6-chlorobenzotriazole, 3,3-di-p-nitrobenzylthiacarbocyanine bromide, 3,3'-di-p-nitrophenylthiacarbocyanine iodide, 3,3- di-o-nitrophenylthiacarbocyanine perchlorate, 3,3'-dimethyl- 9-trifluoromethylthiacarbocyanine iodide, 9-(2,4- dinitrophenylmercapto)-3,3'-diethylthiacarbocyanine iodide, bis(4,6-diphenylpyryl-2)trimethianecyanine perchlorate, anhydro-2-p-dimethylaminophenyliminomethyl-6-nitro-3-(4- sulfobutyl)benzothiazolium hydroxide, l-(2-benzothiazoly)-2 -(p-dimethylaminostyryl)-4,6-diphenylpyridinium iodide, l,3- diethyl-S-l l ,3-neopentylene-6-( l ,3,3-trimethyl-2-indolinylidene)-2,4-hexadienylidenel-2-thiobarbituric acid, 2,3,5- triphenyl-ZH-tetrazolium chloride, 2-(4-lodophenyl)-3-(4- nitrophenyl)-5-phenyl-tetrazolium chloride, l-methyl-8- nitroquinolinium methyl sulfate, 3,6-bisl4-(3-ethyl-2- benzothiazolinylidene)-2-butenylidene]-l,2,4,5-cyclohexanetetrone, Anhydro-6,6-dinitro-3,3'-di(3-sulfopropyl) thiacyanine hydroxide, sodium salt, 1,3-diethyl-l-methyl-2'- phenylimidazo[4,5-b1quinoxaline-3'-indolocarbocyanine iodide, 1 ,3-diallyl-2-[2-(3,5-dimethy1- 1-phenyl-4- pyrazolyl)vinyl]imidazo-[4,5-b]quinoxalinium iodide, 1,3- diethyl-l '-methyl-2'-phenylimidazo[4,5-b]quinoxolino-3'indolocarbocyanine iodide, 3-eithyl-2-[(2-methyl-5-oX0-3- phenyl-3-isoxazolin-4-yl)vinyl]-o-nitrobenzothiazolium methyl sulfate, and the like.

Silver halide grains having a mean grain diameter, i.e., an

average grain size in the range of about .01 to about 2 microns, preferably about 0.2 to about 1 micron, give particularly good results. The silver halide grains can be any suitable shape such as cubic or octahedral. v The direct-positive photographic silver halide emulsions of this invention contain silver halide grains which are fogged. Fogging can be effected by chemically or physically treating the photographic silver halides by methods previously described in the prior art. Such fogging can be accomplished by various techniques such as chemical sensitization to fog, particularly good results being obtained with techniques of the type described by Antoine Hautot and Henri Saubenier in Science et Industries Photographiques, Vol. XXVIII, Jan. 1957, pages 57 to 65. The silver halide grains can be fogged with high intensity light, reduction fogged with a reducing agent such as thiourea dioxide or stannous chloride or fogged with gold or noble metal compounds. Combinations of reduction fogging agents with gold compounds or compounds of another metal more electropositive than silver, e.g., rhodium, platinumor iridiunflcan beused infogging the silver halide grains. The fogged silver halide grains in the direct-positive photographic emulsions of this invention give a density of at least 0.5, when developed without exposure for 5 minutes at 68 F. in Developer A when a direct-positive emulsion containing such grains is coated at a coverage of 50 to about 1,000 mg. of silver per square foot of support.

The direct-positive photographic emulsions of this invention can comprise reduction and gold fogged silver halide grains, i.e., silver halide grains which are fogged with a combination of a reduction fogging agent and a gold fogging agent.

The use of low concentrations of reduction and gold fogging agents in such a combination give unique fogged silver halide grains which are characterized by a rapid loss of fog upon chemical bleaching, as described hereinafter. It is known that one equivalent weight of a reducing agent will reduce one equivalent weight of silver halide to silver. To obtain the fogged silver halide grains which are characterized by a rapid loss of fog upon bleaching, much less than one equivalent weight of reduction fogging is employed. Thus, less than about 0.06 milliequivalents of reduction fogging agent per mole of silver halide is employed in fogging the silver halide grains. Generally, about 0.0005 to about 0.06, preferably about 0.001 to about 0.03 milliequivalents of reduction fogging agent per mole of silver halide is employed in fogging the silver halide grains in the practice of this invention. Higher concentrations of reduction fogging agent can result in a substantial loss in photographic speed. A preferred reduction fogging agent employed in combination with the gold fogging agent, or a compound of another metal more electropositive than silver, is thiourea dioxide which is preferably employed in a concentration in the range of about 0.05 to about 3, most preferably about 0.1 to about 2 milligrams per mole of silver halide or about 0.005 to about 0.03 millimoles per mole of silver halide. Stannous chloride is another suitable reduction fogging agent which is used in practicing this invention and is preferably used in concentrations in the range of about 0.05 to about 3 milligrams of stannous chloride per mole of silver halide. The

use of the reduction and gold fogging agents in low concentration gives direct-positive photographic silver halide emulsions exhibiting outstanding photographic speed. Examples of suitable reduction fogging agents which can be employed in the practice of this invention include hydrazine. phosphonium salts such as tetra(hydroxy methyl)phosphonium chloride, thiourea dioxide, as disclosed in Hillson U.S. Pat. No. 3,062,651 issued Nov. 6, 1962, and Allen et al., U.S. Pat. 2,983,609 issued May 9, 1961, reducing agents such as the stannous salts, e.g., stannous chloride, as disclosed in Carroll U.S. Pat. No. 2,487,850 issued Nov. 15, 1939, polyamines such as diethylene triamine, as disclosed in Lowe et al., U.S. Pat. No. 2,519,698 issued Aug. 15, 1950, polyamines such as spermine, as disclosed in Lowe et al., US. Pat. No. 2,521,925 issued Sept. 12, 1950, bis(B-aminoethyl) sulfide and its water soluble salts, as disclosed in Lowe et al., U.S. Pat. No. 2,521,926 issued Sept. 12, 1950, and the like.

The gold fogging agents employed in practicing this invention can be any gold salt suitable for use in fogging photographic silver halide grains and includes the gold salts disclosed in Waller et al., U.S. Pat. No. 2,399,083 issued Apr. 23, 1946, and Damschroder et al., U.S. Pat. No. 2,642,361 issued June 16, 1953. Specific examples of gold fogging agents are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride, 2-aurosulfobenzothiazole metho chloride, and the like. The concentration of gold fogging agent employed in the practice of this invention is subject to variation, but is generally in the range of about 0.0001 to about 0.01 millimoles per mole of silver halide. Potassium chloroaurate is a preferred gold fogging agent and is often used at concentrations of less than about 5 mg. per mole of silver halide and preferably at concentrations in the range of about 0.05 to about 4 milligrams per mole of silver halide. When a gold fogging agent is used in combination with a reduction fogging agent, the gold fogging agent preferably comprises a major portion of the fogging combination with the ratio of gold fogging agent to reduction fogging agent generally being in the range of about 1:3 to about 20:1, often about 2:1 to about 20: 1. The silver halide grains are preferably fogged using the reduction fogging agent initially and subsequently using the gold fogging agent. However, the reverse order of agents can be used or the reduction and gold fogging agents can be used simultaneously.

In practicing this invention, the silver halide grains can be fogged prior to coating or they can be coated prior to fogging. The reaction conditions during fogging of the silver halide grains are subject to wide variation, although the pH is generally in the range of about 5 to about 7, the pAg is generally in the range of about 6 to about 9 and the temperature is generally in the range of about 40 to about C., most often about 50 to about 70 C. During fogging the silver halide grains can be suspended in a suitable vehicle such as gelatin which is generally employed at a concentration in the range of about 50 to about 200 grams per mole of silver halide.

in one preferred embodiment, the most desirable photographic speed is exhibited by direct-positive photographic emulsions comprising silver halide grains which have a substantially uniform diameter frequency distribution and which are fogged using low concentration of reduction fogging agents and gold fogging agents in combination. Such silver halide grains are characterized by a rapid loss of fog upon chemical bleaching. These grains will lose at least about 25 percent and generally at least about 40 percent of their fog when bleached for 5 minutes at 68 F. in a potassium ferricyanide bleach composition as described hereinafter This fog loss can be illustrated by coating the silver halide grains as a photographic silver halide emulsion on a support to give a maximum density of at least 1.0 when processed for 6 minutes at about 68 F. in Developer A and comparing the density of such a coating with an identical, coating which is processed for 6 minutes at 68 F. in the same developer after being bleached for about 5 minutes at 68 F. in a 0.3 percent aqueous potassium ferricyanide solution. The maximum density of the unbleached coating will be at least 30 percent greater, generally at least 60 percent greater than the maximum density of the bleached coating.

The silver halides of this invention comprise at least 50 mole percent chloride. Preferably, the silver halide emulsions comprise at least 70 mole percent chloride, less than mole percent iodide, and the balance bromide. Silver halide emulsions comprising 100 mole percent chloride have also been found to be quite useful.

In a highly preferred embodiment, the direct-positive emulsions of this invention comprise fogged silver halide grains in combination with .an electron acceptor and a halogen-conducting compound. lmproved photographic properties can be obtained with this combination; for example, the background density of the emulsion can be reduced substantially with this combination. The halogen conductors which give particularly good results in the practice of this invention can be characterized in terms of their polarographic half wave potentials,

i.e., their oxidation reduction potentials determined by polarography. Cathodic measurements can be made with a lXl0molar solution of the halogen conductor in a solvent, for example, methanol which is 0.05 molar in lithium chloride using a dropping mercury electrode with the polarographic half wave potential of the most positive cathodic wave being designated E Anodic measurement can be made with 1X10 molar aqueous solvent solution, for example, methanolic solutions of the halogen acceptor which are 0.05 molar in sodium acetate and 0.005 molar in acetic acid using a carbon paste or pyrolytic graphite electrode, with the voltammetric half peak potential for the most negative anodic response being designated E In each measurement, the reference electrode can be an aqueous silver-silver chloride (saturated potassium chloride) electrode at 20 C. Electrochemical measurements of this type are known in the art and are described in New Instrumental Methods in Electrochemistry, by Delahay, lnterscience Publishers, New York, New York, 1954; Polarography, by Kolthoff and Lingane, 2nd Edition, lnterscience Publishers, New York, New York, 1952; Analytical Chemistry, 36, 2426 (1964) by Elving; and Analytical Chemistry, 30, 1576 (1958) by Adams.

Compounds which can be employed as halogen conductors in the practice of this invention include organic or inorganic compounds having an anodic polarographic half wave potential E less than 0.85 and a cathodic polarographic potential E which is more negative than l.0 (determined according to the IUPAC Convention). A preferred class of halogen-conducting compounds is characterized by an anodic half wave potential which is less than 0.62 and a cathodic half wave potential which is more negative than -1.3. A preferred class of halogen conductors that can be used in the practice of this invention comprises the spectral sensitizing merocyanine dyes having the formula:

where A represents the atoms necessary to complete an acid heterocyclic nucleus, e.g., rhodanine, 2-thiohydantoin and the like, B represents the atoms necessary to complete a basic nitrogen containing heterocyclic nucleus, e.g., benzothiazole, naphthothiazole, benzoxazole and the like, each L represents a methine linkage, e.g.,

and n is an integer from 0 to 2, i.e., 0, l or 2. Specific examples of merocyanine dyes falling within the above formula include:

3-carboxymethyl-5-[( 3-ethyl-2-benzothiazolinylidene)- ethylidenelrhodanine;

3-ethyl-5-l( 4-sulfobutyl)-4( 1H )-pyridylidene l-rhodanine, sodium salt.

3carhoxymethyl-5[l 3-methyl-2( 3H l-thiazolinylidene)lsopropylidenelrhodanine.

3-carbnxvmethyl-5-[3-l sulfopropyl l-2-thiazolinylidene lethylidene rhodanine. sodium salt:

3-carboxymethyl-5-[ 3-ethyl-2-benzoxazolinylidene )-ethylidene]-2-thio-2,4-oxazolidinedione;

l-carboxymethyl-5-[ 3-ethy]-2-benzothiazolinylidene) ethylidene]-3-phenyl-3-thiohydantoin;

4-[( l-ethylnaphtho] l ,2-d[thiazolin-2 ylidene)-1- methylethylidene -3-methyll -(4sulfophenyl)-2-pyrazolin-5- one;

4-[(3-ethyl-6-nitro-2-benzothiazolinylidene)-ethylidene -3- phenyl-Z-isoxazolin-5-one; etc. For a further description of suitable halogen conductors, see Wise Belgian Pat. 695,39l issued Sept. 11, 1967. Suitable procedures for preparing merocyanine dyes are described in Brooker et al., US. Pats. Nos. 2,493,747 and 2,493,748 issued Jan. 10, 1950.

The halogen-conducting compounds employed in practicing one embodiment of this invention referred to above can be used in widely varying concentrations. However, the halogenconducting compounds are generally employed at concentrations in the range of about 25 milligrams to about 20 grams, preferably about to about 1,000 milligrams per mole of silver halide.

As already indicated, the electron-accepting compounds and/orhalogen-conducting compounds described herein can be employed in combination with certain types of high molecular weight organic compounds to achieve an even greater increase in the photographic speed of direct-positive emulsions. These compounds are sulfonated and comprise polynuclear aromatic compounds containing at least one sulfo group. The term polynuclear aromatic" as used herein is intended to mean 2 or more benzene rings fused together (for example, as in naphthalene, pyrene, etc.), or at least 2 benzene rings or aromatic rings directly joined together (for example, as in diphenyl, terphenyl, quaterphcnyl, etc.), or through an aliphatic linkage. Such sulfonated derivatives can conveniently be represented by the following general fonnula:

wherein R represents a polynuclear aromatic group as defined above and M represents a cation such as a hydrogen atom or a water-soluble cation salt group (e.g., sodium, potassium, ammonium, triethylammonium, tn'ethanolammonium, pyridinium, etc.).

lncluded among the sulfonated derivatives of the above formula are the following typical examples:

Calcofluor White-MRThis is the trade name for a bis(striazin-Z-ylamino)stilbene-2,2'-disulfonic acid, sodium salt;

Leucophor BThis is the trade name for a bis(s-triazin-2- ylamino)stilbene-2,2'-disulfonie acid, sodium salt.

Sodium 6-(4-methoxy-3-sulfo-w-phenylacryloyl )-pyrene;

3,4-Bis(4-methoxy-3-sulfobenzamido)-dibenzo-thio-phcne dioxide, sodium salt;

4',4"-Bis(2,4-dimethoxy-5-sulfobenzamido)-p-terphenyl, disodium salt,

Chyrsene-6sulfonic acid, sodium salt;

4,4'-Bis[ 2-phenoxy-4-( 2-hydroxyethylamino)-l ,3 ,S-triazin- 6-ylamino]stilbene-2,2-disulfonic acid, disodium salt.

These sulfonated derivatives may be used in any concentration efi'ective for the intended purpose. Good results are generally obtained by employing the compounds in concentrations in the range of about 0.02 to about 10 grams per mole of silver halide.

The halogen-conducting compounds and/or electron acceptors can also be employed in combination with water-soluble halide salts, e.g., bromide salts, as described in Litzennan Belgian Pat. 695,363 issued Sept. 1 l, 1967.

The silver halide emulsion of a photographic element useful in this invention can contain conventional addenda such as gelatin plasticizers, coating aids, antifoggants such as the azaindines and hardeners such as aldehyde hardeners. e.g., formaldehyde, mucochloric acid, glutaraldehyde bis( sodium bisulfite), maleic dialdehyde, aziridines, dioxane derivatives and oxypolysaccharides.

The silver halide emulsion layer of a photographic element which is useful in the instant invention can contain any of the hydrophilic, water-permeable binding materials suitable for this purpose. Suitable materials include gelatin, colloidal albumin, polyvinyl compounds, cellulose derivative, acrylamide polymers, etc. Mixtures of these binding agents can also be used. The binding agents for the emulsion layer of the photographic element can also contain dispersed polymerized vinyl compounds. Such compounds are disclosed, for example, in U.S. Pat. Nos. 3,142,568 of Nottorf issued July 28, 1964; 3,193,386 of White issued July 6, 1965; 3,062,674 of l-louck, Smith and Yudelson issued Nov. 6, 1962; and 3,220,884 of Houck, Smith and Yudelson issued Nov. 30, 1965; and include the water-insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates and the like.

The silver halide emulsion of a photographic element which is useful in the instant invention can be coated on a wide variety of supports. Typical supports are cellulose nitrate film, cellulose ester film, polyvinyl acetal film, polystyrene film, poly(ethylene terephthalate) film and related films or resinous materials as well as glass, paper, metal and the like. Supports such as paper which are coated with a-olefln polymers, particularly polymers of a-olefins containing 2 or more carbon atoms, as exemplified by polyethylene, polypropylene, ethylene butene copolymers and the like can also be employed.

One of the most convenient ways to develop exposed highcontrast elements of this invention is to process them in a continuous transport processing machine. Such machines are disclosed, for example, in U.S. Pat. Nos. 3,025,779 of Russell and Kunz issued March 20, 1962; 3,078,024 of Sardeson issued Feb. 19, 1963; 3,122,086 of Fitch issued Feb. 25, 1964; 3,149,551 of Cramer issued Sept. 22, 1964; 3,146,173 of Meyer issued Nov. 10, 1964; and 3,224,356 of Fleisher and.

Hixon issued Feb. 21, 1965. In such machines, the element is processed in one continuous motion by transporting it into and out of at least one processing solution. The roller transport processing machine of the type disclosed in the Russell and Kunz patent mentioned above has been found to be especially useful.

The photographic elements of this invention may also contain certain onium slats, such as quaternary ammonium slats, sulfonium slats and phosphonium salts, in order to increase the development rate without adversely affecting the contrast. Such compounds are disclosed for example, in Carroll U.S. Pat. NO. 2,271,623 issued Feb. 3, 1942; Beavers et al., U.S. Pat. No. 2,944,898 issued July 12, 1960, Carroll et al., U.S. Pat. Nos. 2,994,900 issued July 12, 1960; 2,288,226 issued June 30, 1942; 2,275,727 issued Mar. 10, 1942; 2,271,622 issued Feb. 3, 1942; British Pat. 1,067,958 published May 10, 1967; and Piper U.S. Pat. No. 2,886,437 issued May 12, 1959. Concentrations ranging from about 0.01 to about 2.0 grams of onium salt per mole of silver in the silver halide emulsion can be used with good results.

The addition of from about 0.005 to about 2.0 grams of a 3- pyrazolidone per mole of silver in the emulsion will also increase the development rate. The pyrazolidones used to advantage include those disclosed in U.S. Pat No. 2,751,297 of Hood and Crookshank issued June 19, 1956, and represented by the following general formula:

wherein X represents hydrogen or acetyl, R represents a heterocyclic group or an aryl group of the benzene or naphthalene series and R represent hydrogen, an alkyl group or an aryl group of the benzene or naphthalene series and R and R each represents hydrogen or an alkyl group. Examples within this formula include l-phenyl-3-pyrazolidone; 5-

methyl-3-pyrazolidone; 1-phenyl-5-phenyl-3-pyrazolidone; 1- pheny1-5-methyl-3-pyrazolidone; l-pheny1-4,4-dimethyl-3 pyrazolidone; 1-p-hydroxyyphenyl-4,4-dimethyl-3- pyrazolidone; 4-methyl-1phenyl-3-pyrazolidone; etc. The above 3-pyrazolidones may also be contained in a contiguous, layer instead of the silver halide emulsion if desired.

The invention can be further illustrated by the following examples.

EXAMPLE 1 A pure silver chloride photographic emulsion is fogged with 4 mg. of thiourea dioxide per mole of silver. A portion of this emulsion serves as the control sample.

An electron acceptor (l) of the formula l,l'-diethyl-2,2'- cyanine chloride treated with N-bromosuccinimide is added to a sample of the emulsion at a concentration of mg./mole of silver along with 200 mg./mole of silver of a halogen conductor dye of the formula 3-carboxymethyl-5[(3-methyl-2(3 H)-thiazolinylidene)isopropylidene1rhodanine (11). The resulting emulsion is coated on a cellulose acetate film support at a coverage of mg. of silver per ft.

The element is exposed on a scnsitometer and developed in the Kodak D85 Developer for 1.5 minutes at 68 F.

KODAK D-85 DEVELOPER The emulsion sample containing 1 and 11 reverses when exposed solely to blue light and then developed in Kodak D-85 as described above.

EXAMPLE 2 Dye Mg. dye/mole Ag. Rel Speed Dmax Dmin EXAMPLE 3 A silver chlorobromide emulsion is prepared by adding simultaneously nine-tenths mole of sodium chloride, onetenth mole of potassium bromide and one mole of silver nitrate over 50 minutes at 50 C. to a solution of 43 g. of

gelatin. An additional 37 g. of gelatin is added and the emulsion is chill set and washed. The emulsion is then fogged by heating with thiourea dioxide (0.3 mg./Ag mole, 20 minutes at 65 C.), adding potassium chloroaurate (0.2 mg./Ag mole, 50 minutes at 65 C.) and continuing heating until high contrast is obtained and the emulsion develops to maximum density without being exposed.

Before coating, 15 mg. of l-pheny1-4-methyl-3- pyrazolidone/per mole of silver and 400 mg. of the electron acceptor, 1,3-diethyl-l -methyl-2'-phenylimidazo[4,5-b]quinoxoline-3'-indolocarbocyanine iodide (III), are added to the emulsion. The emulsion is coated on a polyester support (polyethylene terphthalate), exposed, and developed 2%minutes in Kodak D-85 Developer, fixed, washed and dried. A direct-positive image with the following characteristics was obtained.

Contrast Dmax Dmin Similar improved results are obtained when the electron acceptors, Anhydro-6,6-dinitro-3,3'-di(3-sulfopropyl)thiacyanine hydroxide, sodium salt, 1,3-diethyl-l -methyl-2' phenylimidazo[4,5-b]quinoxalino-3 -indolocarbocyanine iodide, 1,3-diallyl-2-[2-( 3,5-dimethyll-phenyl-4- pyrazolyl)vinyl]imidazo-[4,5-b]quinoxalinium iodide and 1,3- diethyl-l -methyl-2'-phenylimidazo[4,5-blquinoxolino-3-indolocarbocyanine iodide, are substituted in the above emul- EXAMPLE 4 Feature Rel Speed 7 Dmax Dmin n 100 1.18 2.70 0.82 ll 8: III l 5.50 2.72 0.04 ll & IV B8 4.90 2.74 0.06

The addition of a halogen-conducting dye results in good speed but a poor reversal (high Dmin); the addition of a halogen-accepting dye and an electron-acceptor results in high contrast, low Dmin and a sharp toe.

Similar results are obtained when the halogen-conducting compound, 3-carboxymethyl-5-[ 3( sulfopropyl )-2-thiazolinylidene]ethylidene rhodanine, sodium salt, is substituted as halogen-conducting compound in the above emulsion.

We claim:

1. A process comprising developing an exposed, blue-sensitive-direct-positive, high-contrast photographic element in a photographic developer comprising a silver halide developing agent consisting essentially of a polyhydroxy benzene compound, said photographic element comprising a support coated with a direct-positive silver halide emulsion comprising fogged silver halide grains and an organic compound which accepts electrons which has an anodic polarograph halfwave potential and a cathodic polarograph halfwave potential which, when added together, give a positive sum, wherein said direct-positive emulsion has adsorbed to said fogged grains a halogen-conducting compound having an anodic polarograph halfwave potential less than 0.85 and a cathodic polarograph halfwave potential which is more negative than l .0, wherein said halide is at least 50 mole percent chloride.

2. A process according to claim 1 wherein said halide comprises at least 70 mole percent chloride.

3. The process of claim 1 wherein said halogen-conducting compound is a merocyanine dye.

4. A process according to claim 1 wherein said direct-positive emulsion also contains a sulfonated compound having the formula:

R-SO -,M wherein R represents a polynuclear group and M represents a cation.

5. A process according to claim 1 wherein said polyhydroxybenzene compound is hydroquinone.

6. The process of claim 5 wherein said developer contains a carbonyl bisulfite-amine condensation product.

7. The process of claim 5 wherein said developer contains sodium formaldehyde bisulfite and from about 0.01 to about 0.05 molar of free sulfite ion.

8. A process according to claim 1 wherein said electron-accepting compound is a cyanine dye.

9. A process according to claim 1 wherein said electron-accepting compound is an imidazolquinoxaline dye.

10. A process according to claim 1 wherein said silver halide grains are fogged with a reduction fogging agent and a gold fogging agent.

11. A process according to claim 1 in which the silver halide comprises at least 70 mole percent chloride and the silver halide grains are fogged with about 0.0005 to about 0.06 milliequivalents per mole of silver halide of a reduction fogging agent and about 0.0001 to about 0.01 millimoles per mole of silver halide of a gold fogging agent.

12. A process according to claim 1 comprising developing an exposed, direct-positive, high-contrast photographic element in a photographic developer comprising a silver halide developing agent consisting essentially of a polyhydroxybenzene compound, said photographic element comprising a support and a direct-positive silver halide emulsion comprising fogged silver halide grains and said organic compound which accepts electrons which has an anodic polarograph halfwave potential and a cathodic polarograph halfwave potential which, when added together, give a positive sum, and halogen-conducting compound which has an anodic polarograph halfwave potential less than 0.85 and a cathodic polarograph halfwave potential which is more negative than 1.0, wherein said halide is at least 50 mole percent chloride, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1, upon processing for 6 minutes at about 68 F. in Developer A, has a maximum density which is at least about 30 percent greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in the same developer after being bleached for about 5 minutes at about 68 F. in a 0.3 percent aqueous potassium ferricyanide solution, wherein Developer A has the following composition:

water to l l.

pH of 9.6

13. The process of claim 12 wherein said halogen-conductor compound is a merocyanine dye.

14. A process according to claim 12 wherein said directpositive emulsion also contains a sulfonated compound having the fonnula:

RSO M wherein R represents a polynuclear group and M represents a cation.

15. A process according to claim 12 wherein said electronaccepting compound is a cyanine dye.

16. A process according to claim 12 wherein said electronac'ceptrig compofifidifinimidaiolqiiinoxaline dye.

17. A process according to claim 12 wherein said silver halide grains are fogged with a reduction fogging agent and a gold fogging agent.

- 18. A process according to claim 12 wherein said polyhydroxybenzene compound is hydroquinone.

19. A blue-sensitivedirect-positive, silver halide emulsion comprising fogged silver halide grains in combination with an electron acceptor which has an anodic polarograph halfvvave potential and a cathodic polarograph halfwave potential which, when added together, give a positive sum, and a halogen-conducting compound which has an anodic polarograph halfwave potential less than 0.85 and a cathodic polarograph halfwave potential which is more negative than 1.0, wherein said halide is at least 50 mole percent chloride.

20. A composition according to claim 19 wherein said halogen conductor is a merocyanine dye.

21. A composition according to claim 19 wherein said electron acceptor is a cyanine dye.

22. A composition according to claim 19 wherein said direct-positive emulsion also contains a sulfonated compound having the formula:

RSO M wherein R represents a polynuclear group and M represents a cation.

23. A composition according to claim 19 wherein said direct-positive, silver halide emulsions comprise reduction and gold fogged silver halide grains, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1, upon processing for 6 minutes at about 68 F. in Developer A, has a maximum density which is at least about 30 percent greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in the same developer after being bleached for about 5 minutes at about 68 F. in a 0.3 percent aqueous potassium ferricyanide solution, wherein Developer A has the following composition:

pH of 9.6

Patent No.

PO-1U50 (5/55) Inventofls) October 26, I97

Dated Kirby ILMilton, Bernard D. Illingsworth It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 3, "electron" should read ---electronsi Col 3, line 6, "polyoxytehylene" should read ---polyoxyethylene--.

Col

Col.

Col. W,

line

line

line

line

line

line

line

line

line

line

line

1 ine- "1x1 O should read 1x1 OJ"L "1X1 0 should read ---1 x1 0 "3-eithyl-" should read 3-ethyl- "0.2" should read .O2-.

insert after "hereinafter" "1 X1 0 should read 1 x! 0 "1x10 should read --1x1O" "LL" should be deleted.

"ethylidene 3" should read ---ethyliden e 7-3 "695,391 should read --695, 3

"BH KMTB" uld read ,15e,1

"slats (both occurrences) should read PO-105O UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,615,51 7 Dated October 26, 1 971 Inventor) Kirby M. Milton, Bernard D. lllingswor'th It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[- Page 2 Col. 9, line hL "slats" should read ---salts---.

Col. 9, line LL), "2, 99h, 900" should read ---2,9hh, 900---.

Col. 1 1 lines 1 1 and 1 2, "quinoxaline" should read --quinoxalino---.

Col. 12, line 25, "imidazolquinoxaline" should read ---imidazoquinoXaline---.

Col. 1 2, line 1 5, after "and" insert ---a--- Col. 1 3, line 7, ="imidazolquinoxaline" should read ---imidazoquinoxaline--.

Signed and sealed this 9th day of January 1973.

(SEAL) Attost:

EDWARD M. FLIET(I!HR,.IR Attesting Officer ROBERT GOTTSCHALK Commissioner of Patents 

2. A process according to claim 1 wherein said halide comprises at least 70 mole percent chloride.
 3. The process of claim 1 wherein said halogen-conducting compound is a merocyanine dye.
 4. A process according to claim 1 wherein said direct-positive emulsion also contains a sulfonated compound having the formula: R-SO3M wherein R represents a polynuclear group and M represents a cation.
 5. A process according to claim 1 wherein said polyhydroxybenzene compound is hydroquinone.
 6. The process of claim 5 wherein said developer contains a carbonyl bisulfite-amine condensation product.
 7. The process of claim 5 wherein said developer contains sodium formaldehyde bisulfite and from about 0.01 to about 0.05 molar of free sulfite ion.
 8. A process according to claim 1 wherein said electron-accepting compound is a cyanine dye.
 9. A process according to claim 1 wherein said electron-accepting compound is an imidazolquinoxaline dye.
 10. A process according to claim 1 wherein said silver halide grains are fogged with a reduction fogging agent and a gold fogging agent.
 11. A process according to claim 1 in which the silver halide comprises at least 70 mole percent chloride and the silver halide grains are fogged with about 0.0005 to about 0.06 milliequivalents per mole of silVer halide of a reduction fogging agent and about 0.0001 to about 0.01 millimoles per mole of silver halide of a gold fogging agent.
 12. A process according to claim 1 comprising developing an exposed, direct-positive, high-contrast photographic element in a photographic developer comprising a silver halide developing agent consisting essentially of a polyhydroxybenzene compound, said photographic element comprising a support and a direct-positive silver halide emulsion comprising fogged silver halide grains and said organic compound which accepts electrons which has an anodic polarograph half wave potential and a cathodic polarograph half wave potential which, when added together, give a positive sum, and halogen-conducting compound which has an anodic polarograph half wave potential less than 0.85 and a cathodic polarograph half wave potential which is more negative than -1.0, wherein said halide is at least 50 mole percent chloride, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1, upon processing for 6 minutes at about 68* F. in Developer A, has a maximum density which is at least about 30 percent greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68* F. in the same developer after being bleached for about 5 minutes at about 68* F. in a 0.3 percent aqueous potassium ferricyanide solution, wherein Developer A has the following composition: DEVELOPER A N-methyl-p-aminophenol sulfate 2.59 grams ascorbic acid 10.09 grams potassium metaborate 35.09 grams potassium bromide 1.09 grams water to 1 l. pH of 9.6
 13. The process of claim 12 wherein said halogen-conductor compound is a merocyanine dye.
 14. A process according to claim 12 wherein said direct-positive emulsion also contains a sulfonated compound having the formula: R-SO3M wherein R represents a polynuclear group and M represents a cation.
 15. A process according to claim 12 wherein said electron-accepting compound is a cyanine dye.
 16. A process according to claim 12 wherein said electron-accepting compound is an imidazolquinoxaline dye.
 17. A process according to claim 12 wherein said silver halide grains are fogged with a reduction fogging agent and a gold fogging agent.
 18. A process according to claim 12 wherein said polyhydroxybenzene compound is hydroquinone.
 19. A blue-sensitive-direct-positive, silver halide emulsion comprising fogged silver halide grains in combination with an electron acceptor which has an anodic polarograph half wave potential and a cathodic polarograph half wave potential which, when added together, give a positive sum, and a halogen-conducting compound which has an anodic polarograph half wave potential less than 0.85 and a cathodic polarograph half wave potential which is more negative than -1.0, wherein said halide is at least 50 mole percent chloride.
 20. A composition according to claim 19 wherein said halogen conductor is a merocyanine dye.
 21. A composition according to claim 19 wherein said electron acceptor is a cyanine dye.
 22. A composition according to claim 19 wherein said direct-positive emulsion also contains a sulfonated compound having the formula: R-SO3M wherein R represents a polynuclear group and M represents a cation.
 23. A composition according to claim 19 wherein said direct-positive, silver halide emulsions comprise reduction and gold fogged silver halide grains, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum deNsity of at least about 1, upon processing for 6 minutes at about 68* F. in Developer A, has a maximum density which is at least about 30 percent greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68* F. in the same developer after being bleached for about 5 minutes at about 68* F. in a 0.3 percent aqueous potassium ferricyanide solution, wherein Developer A has the following composition: DEVELOPER A N-methyl-p-aminophenol sulfate 2.59 grams ascorbic acid 10.09 grams potassium metaborate 35.09 grams potassium bromide 1.09 grams water to 1 liter pH of 9.6 